In modern control systems for internal combustion engines, often measuring devices are used for detecting operating variables of the engine or of the motor vehicle. The measuring signals of these devices form the basis for the control of the engine and therefore for the drive power of the motor vehicle. Unwanted operating states of the engine can occur because of malfunctions in the area of these measuring devices. For this reason, the measuring devices must be monitored as to operability. Such a monitoring system acquires significance for electronic engine power control systems (electronic accelerator pedal systems) wherein the power of the engine and therefore the speed and acceleration of the motor vehicle is controlled on the basis of measurement signals from position transducers. The position transducers are for an operator-controlled element, that is, for a power adjusting unit. In the past, various measures for monitoring such position transducers have been proposed.
U.S. Pat. No. 5,370,094 discloses an arrangement wherein the signal of the position transducer, which is connected to a power adjusting unit (a throttle flap), is compared to a measurement signal value for impermissible deviations. The measurement signal value indicates the Load of the engine and represents the position. If a difference between the signal values is detected, then the assumption is made that a fault has occurred in the area of the position transducer and emergency measures are initiated as may be required. It is also suggested to provide redundant position transducers so that the defective sensor can be detected in the sense of a two-out-of-three selection and so that emergency measures can be initiated on the basis of the correct signals. The defective sensor is detected by a comparison of the position signals with respect to each other as well a by a comparison of each of the position signals to the position signal formed on the basis of the load signal as to impermissible deviations.
A monitoring of the position transducers is achieved with the known procedure but the precision of this monitoring can be unsatisfactory because neither the performance of the load signal with reference to the position of the movable element nor the effects are considered which affect the precision of the measuring results such as pulsations and backflows in the intake pipe of the engine or variations of air density as a consequence of changes in elevation above sea level or of the temperature of the intake air.